CAPE TOWN, South Africa — Retired archbishop Desmond Tutu locked eyes with President Barack Obama on Sunday in an emotional moment between two men who have been pioneers for racial progress a world apart.

Tutu greeted Obama with a "welcome home" to the continent where his father was born, and pleaded with the U.S. president to be a leader for peace, especially in the Middle East, who can make all Africans proud.

Obama was visiting the Desmond Tutu HIV Foundation Youth Centre, an after-school program in a community where many young people are infected with the virus that causes AIDS. Obama praised Tutu, a Nobel Peace Prize laureate who helped bring an end to South Africa's racist apartheid rule, as "an unrelenting champion of justice and human dignity."

Tutu then spoke of Obama's re-election last fall as America's first African-American president. "You don't know what you did for our psyche," Tutu said. "You won, and we won."

"Your success is our success. Your failure, whether you like it or not, is our failure," Tutu said, reaching out to touch Obama's arm. Obama chuckled and threw up his arms as if acknowledging his fate.

"We want you to be known as having brought peace to the world, especially to have brought an end to the anguish of all in the Middle East," Tutu said. "We pray that you will be known as having brought peace in all of these places where there is strife. You have brought peace and no need for the Guantanamo Bay detention center" in Cuba, where the U.S. has detained dozens of suspected terrorists.

In a diplomatic tour full of scripted formality, the 81-year-old archbishop spoke so slowly and passionately that many in the room who work at the center or the White House were moved to tears. "We are proud of you. You belong to us," Tutu concluded.

Obama also may have appreciated such affirming words at a time when he seems to be under constant criticism at home. Obama rose and helped Tutu to his feet, and the two heartily embraced, with the click of media cameras the only sound in the room.

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Obama gave lessons in stage performance to an aspiring teenage rapper after meeting 15-year-old Aviwe Mtongana, who was making music on a Tutu center computer.

The boy identified himself as a rapper and Obama urged the boy, also known as Katmeister, to "give me a little sample."

Mtongana initially demurred, then pushed back his chair and stood up. A grinning Obama said Mtongana must need to "loosen up," and the president demonstrated stretching out his arms like a boxer preparing for a fight.

"Heading to the goal with something failing, now you face the hardest living," Mtongana continued. "Getting out there is not pimping, the real way is through rapping."

Obama declared the performance "outstanding," but offered a word of advice.

"You've got to drop the mic," he said, holding his arm out to the side and opening his fist as though he were dropping a microphone on the ground.

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Obama prematurely aged his daughter Malia by a few days.

He said in a speech at the University of Cape Town that she is "now 15." But the fact of the matter is Malia doesn't turn 15 until Thursday. She was born on the Fourth of July.

Malia might have appreciated the premature aging, since most teens cannot wait to grow up.

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Before the speech, Obama and his family toured the Robben Island prison where Nelson Mandela spent nearly 20 years as a political prisoner before he was released and elected South Africa's first black president.

Obama spent more than 20 minutes inside the tiny cell that housed Mandela for 18 years.

After his family left, Obama remained alone inside the cell that now is a monument to Mandela, a man Obama says is a "personal hero." The president gazed out of a large window with thick white bars. He picked up and examined a small, metal bowl that sat on a small, wooden table before turning his attention to a thin mat with pillows and a brown blanket, on which Mandela would have slept.

Obama visited Robben Island in 2006, when he was a U.S. senator, but the tour was a first for his wife, Michelle, and daughters, Malia and Sasha.

"There was something different about bringing my children," Obama said, opening his speech at the university. He said they now appreciate more the sacrifices that Mandela and others had made for freedom. "I knew this was an experience they would never forget," Obama said.

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Before leaving the island, Obama signed the prison's guest book with a message likely to be seen by the countless visitors who will follow him.

The large book sat open on a simple wooden desk, in a courtyard rimmed by a high concrete wall topped with barbed wire. U.S. Secret Service agents made use of an old guard tower, staffing it with sharpshooters who scanned the horizon with binoculars. The prison was closed to the public for Obama's visit.

Obama, casually dressed in a blue shirt with rolled-up sleeves and khaki slacks, leaned over the desk and wrote for several minutes with first lady Michelle Obama at his side. She signed her name, too.

"On behalf of our family, we're deeply humbled to stand where men of such courage faced down injustice and refused to yield," the president wrote. "The world is grateful for the heroes of Robben Island, who remind us that no shackles or cells can match the strength of the human spirit."

Obama copied his message from a piece of typewritten paper an aide had set down on the book before the president came into the courtyard. He wrote slowly in cursive, apparently not wanting to make a mistake. He left behind the black marker he used to write the message, as well as the note he worked from.

Poor seamanship and flaws in keeping watch contributed to a collision between a Navy destroyer and a commercial container ship that killed seven sailors, Navy officials said, announcing that the warship captain will be relieved of command and more than a dozen other sailors will be punished.